The usual form of a helical resonator filter consists of several helical coils, each wound in the form of a helix, a conductive shell or housing having cavities, each cavity separated by a separating wall from the adjacent cavity and each cavity having a helical coil. The separating wall is apertured to provide an electromagnetic coupling between adjacent helical coils. An inherent characteristic of a conventional helical resonator is that the bandwidth of the filter is determined by the size of the helical coil, the cavity and the coupling apertures. The other words, the maximum bandwidth that can be provided by the helical resonator filter is set by the geometry of the elements that constitute the resonator. In many applications it is desirable to widen the bandwidth without changing the physical size of the resonator or any components thereof.